Mostly Good News for Monarch Spring Migration

AUSTIN, Texas — Millions of monarch butterflies have begun their annual spring migration north into Texas, and entomologists say it’s mostly good news this year. All the monarchs in North America east of the Rocky Mountains winter in one mountainous region of central Mexico, where monarch numbers dropped alarmingly due to a severe snow storm in 2004. Scientists say monarch numbers in this region now appear to have bounced back to approximately 300 million butterflies.

While thousands of monarchs can be seen concentrated in a single time and place during the fall migration in Texas, the spring migration, by contrast, is a more dispersed and drawn out affair lasting nearly two months. Generally, observations of less than 20 monarchs are reported for any one time and location in the spring.

As with many native wildlife species, plants and habitat types hold the key to whether people will see monarchs.

“Native milkweed plants that the monarchs will seek out for egg laying include green milkweed (Asclepias viridis), Zizotes milkweed (Asclepias oenotheroides), and antelope horn milkweed (Asclepias asperula),” said Mike Quinn, an entomologist with the Texas Parks and Wildlife Department, who added that native flowering species like Texas mountain laurel are a favored nectar source for the returning butteries.

Scientists with the Monarch Watch international research and conservation venture report that on Feb. 27 it was apparent the butterflies were leaving Mexico. Until late March, the overwintering generation will be moving through Texas. The next leg of the migration will then be taken up by the first spring generation moving through Texas in April.

“Part of the good news this year is the monarchs are in great shape,” said Chip Taylor with the University of Kansas, where Monarch Watch is based. “The proportion of monarchs with tattered wings and low fat reserves appears to be low. The winter was mild and the result seems to be that those surviving the winter are well prepared for the 600 or so miles they need to travel to reach the milkweed areas of Texas. The peak of returning monarchs is usually sighted in Texas after March 15.”

Taylor said more good news is that scientists were able to purchase more than 500 tags to track butterfly movements, and it appears they have finally recovered most of the tags that were being held by residents of the Mexico protected butterfly reserve after the massive winter kills of 2002 and 2004. Monarch Watch recently offered a 50 peso reward for each tag turned in, which greatly increased the number of tags recovered, but strained the organization’s budget in the process.

Taylor said when scientists and volunteers arrived in Mexico this year, President Felipe Calderón held a meeting at which he announced a “zero tolerance” policy for illegal logging together with a Conservation Development Strategy for the state of Michoacan. In spite of Mexican efforts, Taylor said some illegal logging continues within the 56,000-hectare Monarch Biosphere Reserve, including sites previously occupied by butterflies. Officials hope economic development programs will enable loggers to transition to legal income-producing activities and help prevent illegal logging that is reducing the butterfly’s wintering habitat.

More information, including video and photos of monarch butterflies in Mexico, can be found on the Monarch Watch Web site.